Beef tallow is suitable as a primary lipid source in juvenile Florida pompano feeds

It is assumed that Florida pompano have dietary EPA (20:5n‐3) and DHA (22:6n‐3) requirements. However, it is unclear whether both are equally important in meeting demand for n‐3 long‐chain polyunsaturated fatty acids (LC‐PUFAs) or whether the requirement(s) can be influenced by other fatty acids. Accordingly, we assessed production performance and tissue composition of juvenile Florida pompano (41.0 ± 0.5 g) fed diets containing fish oil; beef tallow; or beef tallow partially or fully supplemented with EPA, DHA or both. After 8 weeks, no signs of fatty acid deficiency were observed. Although fish performance did not vary significantly among the dietary treatments, fish fed the DHA‐supplemented feeds exhibited numerically superior growth than those fed the other diets. Fillets of fish fed the beef tallow‐based diets contained reduced levels of n‐3 fatty acids and LC‐PUFAs and elevated levels of MUFAs and n‐6 fatty acids, although dietary supplementation with EPA and/or DHA attenuated these effects somewhat. Our results suggest that beef tallow is suitable as a primary lipid source in Florida pompano feeds and n‐3 LC‐PUFA requirements may be met by as little as 4 g/kg EPA and 4 g/kg DHA. However, there may be value in supplementing tallow‐based diets with DHA to enhance tissue levels and possibly growth.     

Growth Performance and Proximate and Fatty Acid Compositions of Channel Catfish, Ictalurus punctatus, Fed for Different Duration with a Commercial Diet Supplemented with Various Levels of Menhaden Fish Oil

A 15‐wk study was conducted to evaluate the effect of supplemental menhaden fish oil levels and feeding duration on growth performance and tissue proximate and fatty acid (FA) compositions of juvenile channel catfish, Ictalurus punctatus. Dietary fish oil levels had no effect on final weight gain, feed efficiency, and survival of channel catfish. Tissue lipid contents were directly correlated to dietary lipid levels, while moisture contents were inversely related to dietary lipid levels. Fillet moisture contents progressively decreased, whereas fillet lipid increased with increasing feeding duration. Significant increase in saturated and total n‐3 FAs and decrease in monoenoic and total n‐6 FA in whole body and fillet were observed at each incremental level of dietary fish oil. Percentages of n‐3 and n‐3 highly unsaturated fatty acids in fillet of fish fed the control and 3% fish oil diets decreased with increasing feeding periods, whereas those of fish fed 6 or 9% added fish oil diets remained stable or increased. Ratios of n‐3/n‐6 were statistically comparable throughout the 15‐wk feeding. When expressed in terms of mg/g of fillet, the highest concentration of n‐3 was obtained in fillets of fish fed the 9% added fish oil diet for 15 wk.     

Estimating digestible protein requirements of silver perch, Bidyanus bidyanus Mitchell

In this study, we estimated requirements for digestible protein, using intact protein sources, at one digestible energy content. Using digestibility data for silver perch (Bidyanus bidyanus Mitchell) for a large number of ingredients, we formulated a ‘summit’ diet to contain between 1.4 and 1.8 times the ‘expected requirements’ for digestible essential amino acids (based on requirements for channel catfish, Ictalurus punctatus Rafinesque). A ‘diluent’ diet was formulated to contain 0.4–0.5 times the expected requirements of digestible essential amino acids. Both ‘summit’ and ‘diluent’ diets contained similar digestible energy (14.7 MJ digestible energy kg^?1 for the summit and 13.4 MJ digestible energy kg^?1 for the diluent). Six diets were prepared with the following amounts of summit–diluent diets: 100:0, 80:20, 60:40, 40:60, 20:80 and 0:100. A practical diet widely used by commercial farmers was also included as a control. Ten juvenile fish (2.1–2.6 g) were stocked into each experimental 70‐L acrylic aquarium, and each dietary treatment was randomly assigned to five replicate aquaria. Fish were fed twice daily to apparent satiation for 54 days. Final individual fish weight ranged from 4–15.5 g. Results were analysed using intersecting linear regression analysis. The optimum digestible dietary protein for diets with 13.4–14.7 MJ digestible energy kg^?1, after which protein deposition did not increase significantly, was 28%. Although this study did not determine requirements for individual amino acids, for diets with the digestible energy content used here, requirements for individual amino acids obviously did not exceed the content in the 28% protein diet. These contents are useful as an estimate of ‘recommended levels’ for silver perch diets with 13.4–14.7 MJ digestible energy kg^?1. The proximate composition of fish was affected by diet. Whole body protein and moisture increased, whereas lipid content decreased with increasing dietary protein content (and increasing protein–energy ratio and decreasing lipid). Fish size was also affected by diet; however, the changes in whole carcass proximate composition also occurred for fish fed diets 60:40, 80:20 and the summit diet which were a similar final weight.     

The influence of environmental temperature on the apparent nutrient and fatty acid digestibility in Atlantic salmon (Salmo salar L.) fed finishing diets containing different blends of fish oil, rapeseed oil and palm oil

A 12‐week feeding trial was conducted to investigate the interactive effects between water temperature and diets supplemented with different blends of fish oil, rapeseed oil and crude palm oil (CPO) on the apparent nutrient and fatty acid digestibility in Atlantic salmon. Two isolipidic extruded diets with added fish oil fixed at 50% and CPO supplemented at 10% or 25% of total added oil, at the expense of rapeseed oil, were formulated and fed to groups of Atlantic salmon (about 3.4 kg) maintained in floating cages. There were no significant effects (P>0.05) of diet on growth, feed utilization efficiency, muscle total lipid or pigment concentrations. Fatty acid compositions of muscle and liver lipids were mostly not significantly different in salmon fed the two experimental diets but showed elevated concentrations of 18:1n‐9 and 18:2n‐6 compared with initial values. Decreasing water temperatures (11–6°C) did not significantly affect protein, lipid or energy apparent digestibilities of the diets with different oil blends. However, dry matter digestibility decreased significantly in fish fed the diet with CPO at 25% of added oil. Increasing dietary CPO levels and decreasing water temperature significantly reduced the apparent digestibility (AD) of saturated fatty acids. The AD of the saturates decreased with increasing chain length within each temperature regimen irrespective of CPO level fed to the fish. The AD of monoenes and polyunsaturated fatty acids was not affected by dietary CPO levels or water temperature. No significant interaction between diet and water temperature effects was detected on the AD of all nutrients and fatty acids. The results of this study showed that the inclusion of CPO up to about 10% (wt/wt) in Atlantic salmon feeds resulted in negligible differences in nutrient and fatty acid digestibility that did not affect growth performance of fish at the range of water temperatures generally encountered in the grow‐out phase.     

Effects of feeding diets containing various dietary protein and lipid ratios on the growth performance and pigmentation of post-juvenile coho salmon Oncorhynchus kisutch reared in sea water

Six extruded dry diets formulated to contain one of two levels of digestible protein (37% or 44%) and one of three levels of digestible lipid (16%, 23% or 30%) on a dry weight basis and a seventh diet (commercial control) were used to feed triplicate groups of post‐juvenile coho salmon Oncorhynchus kisutch in sea water. Fish were fed to satiation twice daily for 168 days. Growth performances were monitored every 28 days. On day 168, samples were taken from each replicate group per dietary treatment for determinations of whole‐body and muscle proximate compositions. Fatty acid compositions and astaxanthin concentration in both the experimental diets and fish flesh were assessed by gas chromatography (GC) and high‐performance liquid chromatography (HPLC) respectively. Coho salmon fed diets containing the higher lipid levels (23–30%) exhibited improved feed efficiency, protein efficiency ratio, percentage protein deposition and percentage gross energy utilization. Higher protein content diets supported better growth than those that had lower protein content, but the former led to lowered protein efficiency ratio, percentage protein deposition and gross energy utilization. Fish fed the diets with high lipid levels (23% or 30%) also had higher astaxanthin content in raw flesh.     

Protein and Energy Levels for Maximum Growth, Diet Utilization, Yield of Edible Flesh and Protein Sparing of Hybrid Clarias Catfish (Clarias macrocephalus×Clarias gariepinus)

Abstract— Two feeding trials were performed to determine dietary protein and energy levels for maximum growth, diet utilization, yield of edible flesh and protein sparing of hybrid Clarias catfish ( Clanas macrocephalus × Clarias gariepinus ). A 3 × 3 factorial design was employed for experiment 1 in which nine diets containing either 20, 30 or 40% protein and 275, 300 or 325-kcal digestible energy/100 g were used. The follow-up experiment 2 was a 3 × 2 factorial in which three protein levels (30, 35 and 40%) and two digestible energy levels (275 and 325 kcal/100 g) were tested. Dietary ingredients used in both studies were similar but the ratios of energy provided by dextrin and lard were 11.3/1.0 and 3.8/1.0 for experiments 1 and 2, respectively. Each of the experimental diets was fed to apparent satiation twice daily to three aquaria of fish (15 fish/aquaria) with average weight of 4.0 and 2.0 g for experiment 1 and 2, respectively, for 8 wk. Performance of fish in experiment 1 was mainly influenced by dietary protein rather than by energy levels. Maximum growth and diet utilization were attained at dietary protein and energy levels of 40% and 275 kcal/100 g, respectively. Energy levels did not spare dietary protein in experiment 1. In experiment 2, growth, diet utilization, and yield of edible flesh of fish were influenced by protein and energy levels. Furthermore, the protein sparing effect was observed in experiment 2. Best performance and protein sparing were found at 35% protein and 325-kcal digestible energy/100 g. The studies showed that dietary protein and energy requirement for hybrid Clarias catfish are affected by carbohydrate to lipid ratio. Fish utilize dietary energy with a dextrin to lard ratio of 3.8/1.0 more efficiently than that with a ratio of 11.3/1.0. Therefore, dietary protein and energy for best performance and protein sparing of hybrid Clarias catfish reported for experiment 2 were more appropriate.     

Effects of six alternative lipid sources on growth and tissue fatty acid composition in Japanese sea bass (Lateolabrax japonicus)

Ten-week experiment was carried out on Japanese sea bass (5.87 ± 0.02 g) to study the effects of replacement of fish oil with six alternative lipid sources: pork lard, PL; beef tallow, BT; poultry fat, PF; soybean oil, SO; corn oil, CO; and a mixed-fat (MF: tallow, 60%; soy oil, 20%; fish oil, 20%) on growth performance and fatty acid (FA) composition in fillet and liver. Seven isoenergetic and isonitrogenous experimental diets were formulated, containing 10% of added lipid. Fish oil was used in control diet, which was substituted by 50% with the alternative lipid sources in the other six diets.

Weight gain (WG), specific growth rate (SGR), Feed conversion ratio (FCR) feed intake and hepatosomatic index (HSI) of fish fed the experimental diets were not significantly different (P > 0.05). Protein efficiency ratio (PER) in fish fed the PF diet were significantly lower than those of fish fed SO and CO diets. Significant differences in carcass moisture and lipid contents of carcass and liver were observed among fish fed the dietary treatments. Generally, the fatty acid composition of fish fillets and livers reflected the dietary FA composition.     

Influence of different dietary lipid sources on the growth,tissue fatty acid composition,histological changes and peroxisome proliferator‐activated receptor γ gene expression in large yellow croaker (Pseudosciaena crocea R.)

A 9‐week feeding trial was conducted to investigate the impact of dietary lipid sources on the lipid mechanisms of large yellow croaker by feeding three isonitrogenous and isoenergetic diets containing fish oil (FO), soybean oil (SO) and beef tallow (BT) respectively. The effects of the diets on the growth performance, somatic indices, tissue fatty acid composition, histological changes and peroxisome proliferator‐activated receptor (PPAR)γ expression were evaluated. Experimental diets were all well accepted by fish and no significant (P>0.05) differences were found in the weight gain, growth rate and feed conversion rate. The fatty acid profile of the fish fillet and liver reflected the fatty acid composition of the diets. Specific‐fatty acids were selectively retained, however, in the flesh of the fish; in particular, docosahexaenoic acid and arachidonic acid concentrations were higher than the dietary concentrations. When FO was replaced by SO or BT diets, the reduction in eicosapontaenoic acid in fish tissue was more pronounced, suggesting a preferred utilization of this fatty acid. The consumption of SO displayed intense lipid accumulation in the liver of the fish. The expression of PPARγ increased significantly in the SO group compared with the FO and BT groups (P<0.05).     

Partial replacement of fish oil by flaxseed oil in Atlantic halibut (Hippoglossus hippoglossus L.) diets: effects on growth,nutritional and sensory quality

Three isonitrogenous (520 g protein kg^?1 DM) and isoenergetic (25 MJ kg^?1 DM) diets containing increasing levels of flaxseed oil (FxO; 0%, 40% and 70% of total added oil) at the expense of fish oil (FO) were tested for 33 weeks in groups of 61 individually PIT‐tagged halibut (initial weight, 849 ± 99 g). Effects on fish growth performance, fillet nutritional and sensory quality were determined. Specific growth rate (0.2% day^?1), feed conversion ratio (1.2–1.3) and nitrogen and energy retention were not affected by dietary treatments. Dietary fatty acid composition was reflected in fatty acid profiles of halibut muscle, liver and heart. Muscle of fish fed FxO diets contained higher 18:2n‐6 and 18:3n‐3 concentrations whereas 20:5n‐3 and 22:6n‐3 levels were significantly reduced. However, increasing FO replacement induced preferential retention of 22:6n‐3 especially in heart, and a trend for 20:5n‐3 conservation in heart and muscle was observed. FO replacement did not affect colour, texture and the characteristic fish odour and flavour of cooked fillets. By selectively retaining long‐chain polyunsaturated fatty acids halibut can adapt to a lower dietary supply without adverse effects on growth, feed conversion ratio, survival, and fillet nutritional and sensory quality.     

饲料低蛋白、高脂肪和高消化能对斑点叉尾鮰

为了探讨高脂肪条件下不同的蛋白和能量水平对斑点叉尾鮰生长及体组成的影响,试验设2个蛋白水平(22%,28%),2个脂肪水平(10.0%,14.0%),2个消化能水平(12.56 kJ/g,14.23 kJ/g),共8组,分别为P28L10E14.23,P28L14E14.23,P22L10E14.23,P22L14E14.23,P28L10E12.56,P28L14E12.56,P22L10E12.56和P22L14E12.56。试验饲料配方使用鱼粉和豆粕调节蛋白含量,混合油脂(鱼油∶玉米油=1∶1)调节脂肪含量,α-淀粉、次粉和麸皮调节消化能含量,并以微晶纤维素为填充物,每组3个重复,每个重复20尾鱼(141.5?1.0) g。饲养60 d后,进行生产性能测定,并采集组织样本,测定相关指标。结果表明,鱼体末重(FW)、增重率(WG)、特定生长率(SGR)和饵料系数(FCR)不受饲料蛋白、脂肪和消化能单一营养水平影响(P>0.05);但与饲料蛋白、脂肪和消化能三者的交互作用(P<0.01)有关。胴体蛋白、脂肪含量与饲料脂肪和消化能水平相关(P<0.05)。由此可见,饲料过高脂肪和消化能对斑点叉尾鮰没有额外的促生长作用;饲料蛋白水平达到22%时,即可满足140~300 g斑点叉尾鮰的营养需要;饲料中22%的蛋白、10%的脂肪、12.56 kJ/g的消化能即可满足斑点叉尾鮰仔鱼的生长需要,同时又能保证其正常生理机能,建议可在实际生产配方中作参考值。     

Growth and efficiency of feed usage by Atlantic salmon (Salmo salar) fed diets with different dietary protein: Energy ratios at two feeding levels

The effect of dietary digestible protein/digestible energy (DP/DE) ratios and feeding level on growth, feed efficiency, nutrient and energy usage by Atlantic salmon ( Salmo salar ; initial body weight, 7.0 g/fish) at 15°C was investigated in a 16-week feeding trial. Three diets, differing in their DP and DE contents, namely 37/18 (regular diet, RD), 37/21 (high fat diet, HF) and 44/ 22 (high nutrient-dense diet, HND) g/MJ of dry feed were formulated. DP/DE ratios were 20, 18 and 20 g/MJ for the RD, HF and HND diets, respectively. Salmon were hand-fed three times a day at either 100% or 85% of the feed requirement estimated by a bioenergetics model. At each feeding level, DE intake (kJ/fish) was similar for all three diets. Diet composition did not affect growth rate. However, increasing the digestible energy density from 18 to 22 MJ/kg of dry feed resulted in a significant increase ( P  < 0.05) in feed efficiency. Restricting feed intake significantly decreased live body weight gains for all diets. However, feed efficiency was not affected by feeding level. Diet composition and feeding level did not affect carcass composition and nutrient and energy usage, with the exception of a higher ( P  < 0.05) carcass lipid of fish fed the HF100 diet compared with the fish fed the RD and HND diets and a higher ( P  < 0.05) lipid gain (g/fish) of fish fed the HF100 diet compared with fish fed all the diets at the restricted feeding level. Restricting feeding resulted in significantly lower ( P  < 0.05) energy gain (kJ/fish) compared with fish fed at 100%. Increasing the DE and nutrient density of the diet had no effect on growth but improved feed efficiency and lowered solid wastes (g of solid wastes per kg of fish produced) while dissolved wastes were not affected by dietary ormulation.     

Influence of terrestrial lipid and protein sources and activated carbon‐treated fish oil on levels of persistent organic pollutants and fatty acids in the flesh of Atlantic salmon

Reductions in flesh contaminant concentrations were evaluated in a 36‐week feeding trial examining several dietary techniques. Atlantic salmon were fed one of seven dietary treatments for 24 weeks. These diets included a fishmeal, fish oil control diet, an industry control diet, three diets that examined a 75% replacement level of anchovy oil (AO) with flaxseed oil, canola oil and poultry fat, and two diets formulated to be low in contaminants formulated with canola oil, activated carbon‐treated anchovy oil and canola protein concentrate or soy protein concentrate. Following this initial 24‐week feeding interval, a 12‐week finishing diet was utilized to restore the levels of omega‐3 highly unsaturated fatty acids (n‐3 HUFAs). The salmon had marked reductions in their flesh concentrations of total polychlorinated biphenyls (PCBs), dioxin‐like PCBs and total toxic equivalents by the end of the grow‐out phase, but also exhibited significant depressions in their flesh concentrations of n‐3 HUFAs relative to 100AO‐fed fish. The 12‐week finishing diet period was effective in partially re‐instating omega‐3 levels to those present in the flesh lipids of fish fed 100AO while concurrently maintaining lower flesh contaminant concentrations.     

饲料中可消化淀粉对大口黑鲈生长、体组成和非特异性免疫指标的影响

配制6种不同可消化淀粉水平(5.93%、8.71%、11.96%、15.11%、18.16%、21.74%)的等氮和等脂肪的饲料,以试验鱼的生长、饲料效率、体组成、血糖及非特异性免疫和血液学参数作指标,评定大口黑鲈饲料中可消化淀粉的适宜水平。用上述6种饲料饲喂初始体质量(28.36 ± 0.10)g 的大口黑鲈48 d,每饲料设3个重复,每重复35尾鱼。采用表观饱食投喂,每天饲喂2次(8:00和16:00)。结果显示,饲料中可消化淀粉水平为21.74%时,大口黑鲈成活率最低;可消化淀粉水平超过8.71%时,鱼体终末体质量、特定生长率和摄食量均显著下降;但饲料效率和蛋白质效率在可消化淀粉水平为11.96%时达到最高。随着饲料中可消化淀粉水平的升高,饲料的蛋白质消化率差异不显著,但脂肪和淀粉的消化率显著降低;全鱼、肌肉、内脏及肝脏的蛋白质含量均显著降低,而水分含量显著升高,脂肪含量在8.71%组达到最高后又显著降低;肝体比、脏体比、肝糖原及血清谷丙转氨酶和谷草转氨酶的活性均显著升高。饲料中可消化淀粉水平高于11.96%时,试验鱼餐后6至12 h呈现持续的高血糖症状;血清蛋白质含量和血清补体活性在可消化淀粉为8.71%时达到最高;而血清溶菌酶活性和头肾白细胞呼吸爆发活性在11.96%组达到最高。另外,红细胞数和红细胞压积未受到饲料中可消化淀粉水平增高的显著影响,但血红蛋白含量显著降低。综合大口黑鲈的生长、饲料效率、体组成、血糖和非特异性免疫指标得出,大口黑鲈对饲料中可消化淀粉的利用与耐受力有限,饲料中可消化淀粉的适宜水平为8.71% ~ 11.96%。     

Dietary lipid sources for seabream and seabass: growth performance, tissue composition and flesh quality

Due to its traditionally good availability, digestibility and high content of n ? 3 HUFA, fish oil is the main lipid source in fish feeds. However, world demand for this product has grown significantly in recent years, whereas its production, based on fisheries landings, is static. The purpose of the present study was to assess the effect of partial replacement of fish oil in compound diets for gilthead seabream and seabass, by several vegetable oil sources, on growth, dietary fatty acid utilization and flesh quality. Five iso‐energetic and isoproteic experimental diets were formulated (25% lipid content). Fish oil was the only added lipid source in the control (FO) diet, and it was included in the other experimental diets at a level high enough (40% of FO diet) to keep the n ? 3 HUFA levels well over 3% in order to cover the essential fatty acid requirements of these species. Fish oil was replaced by soyabean oil (SO), rapeseed oil (RO) and linseed oil (LO) or a mixture (Mix) of them. Feed intake in all dietary groups was in the range of results obtained for commercial diets in both species, and growth and feed utilization were very good. The results show that, providing a minimum content of essential fatty acids in the diet, it is possible to replace up to 60% of the fish oil by SO, LO and RO or a mixture of them in diets for seabream and seabass, without compromising fish growth. Fatty acid composition of liver and muscle reflected that of the diet, but utilization of dietary lipids differed between these two tissues and was also different for the different fatty acids. Despite reduction in dietary saturated fatty acids by the inclusion of vegetable oils, their levels in fish liver were as high as in fish fed the fish oil diet, whereas, in muscle, levels were reduced according to that in the diet. Linoleic and linolenic acids were accumulated in the liver proportionally to their levels in the diet, suggesting a lower oxidation of these fatty acids in comparison to other 18C fatty acids. Regarding eicosapentaenoic acid (20 : 5n ? 3; EPA), docosahexaenoic acid (22 : 6n ? 3; DHA) and arachidonic acid (20 : 4n ? 6; ARA), these essential fatty acids were reduced in the liver at a similar rate, whereas DHA was preferentially retained in the muscle in comparison with the other fatty acids, denoting a higher oxidation particularly of EPA, in the muscle. Some other PUFA increased despite their low dietary levels in seabream fed LO diets and in seabass fed SO diet, suggesting the stimulation of delta‐6 and delta‐5 desaturase activity in marine fish. Despite differences in fatty acid composition, fillet of fish fed vegetable oils was very well accepted by trained judges when assessed cooked.     

The effect of dietary energy level on growth and nutrient utilization by juvenile diploid and triploid brook charr,Salvelinus fontinalis

Triploids are used in aquaculture because they are sterile and do not undergo preharvest loss in flesh quality. Despite this advantage, they do not always perform as well as diploids when fed commercial diets. This study investigated whether differences in dietary energy utilization might explain this reduced performance. Dietary lipid levels were adjusted to supply diets with 22.7, 23.6 or 24.4 MJ kg^?1 gross energy and fed to juvenile diploid and triploid brook charr. Fish were fed to satiation twice daily in a 70‐day growth trial, with samples collected at days 0 and 70 for proximate composition and plasma insulin‐like growth factor I (IGF‐I) analysis. This was followed by a digestibility trial using the same diets to determine apparent digestibility coefficients. Triploids had lower growth rates and condition factor than diploids on all three diets, but there was no effect of ploidy on feed conversion efficiency. Triploids also had lower whole‐body lipid content, but equal protein content, which resulted in lower energy content at both days 0 and 70. There was no effect of diet or ploidy on plasma IGF‐I concentrations. Triploidy did not affect diet digestibility, suggesting that the reduced performance of triploids is due to a difference in metabolism and energy utilization.     

Effect of Dietary Protein Concentration on Growth and Processing Yield of Channel Catfish Ictalurus punctatus1

Abstract.— This study was conducted to evaluate the effect of dietary protein concentration and an all‐plant diet on growth and processing yield of pond‐raised channel catfish Ictalurus punctatus. Four diets were formulated using plant and animal proteins to contain 24%n, 28%, 32%, or 36% crude protein with digestible energy to protein (DE/P) ratios of 11.7, 10.2, 9.0, and 8.1 kcal/g, respectively. An all‐plant diet containing 28% protein with a DE/P ratio of 10.2 kcal/g was also included. Channel catfish fingerlings averaging 40 g/fish were stocked into 24, 0.04‐ha ponds at a density of 18,530 fish/ha. Five ponds were used for each dietary treatment except for the all‐plant diet which had four replicates. The fish were fed once daily to apparent satiation for 160 d. No differences were observed in feed consumption, weight gain, survival, carcass and nugget yield, or fillet moisture and protein concentrations among treatments. Fish fed the 28% protein diet had a lower feed conversion ratio (FCR) than fish fed diets containing 24% and 32% protein, but had a FCR similar to fish fed the 36% protein diet. Fillet yield was higher for fish fed the 36% protein diet than fish fed the 24% protein diet. Visceral fat was lower in fish fed the 36% protein diet than fish fed other diets. Fish fed the 32% and 36% protein diets exhibited a lower level of fillet fat than fish fed the 24% protein diet. The 36% protein diet resulted in a lower level of fillet fat than fish fed the 28% protein diet. There was a positive linear regression in fillet yield and fillet moisture concentration and a negative linear regression in visceral fat and fillet fat against dietary protein concentration. No differences in any variables were noted between the 28% protein diets with and without animal protein except that fish fed the 28% protein diet without animal protein had a higher FCR than fish fed the 28% protein diet with animal protein. This observation did not appear to be diet related since FCR of fish fed the 32% protein diet containing animal protein was not different from that of fish fed the 28% all‐plant protein diet. Data from the present study indicate that dietary protein concentrations ranging from 24% to 36% provided for similar feed consumption, growth, feed efficiency, and carcass yield. However, since there is a general increase in fattiness and a decrease in fillet yield as the dietary protein concentration decreases or DEP ratio increases, it is suggested that a minimum of 28% dietary protein with a maximum DEIP ratio of 10 kcal/g protein is optimal for channel catfish growout.     

Inclusion of rendered animal ingredients as fishmeal substitutes in practical diets for cuneate drum, Nibea miichthioides (Chu, Lo et Wu)

Potential of using rendered animal ingredients, poultry by‐product meal (PM), meat and bone meal (MBM), feather meal (FM) and blood meal (BM) to replace fishmeal in practical diets for cuneate drum Nibea miichthioides (Chu, Lo et Wu) was examined in a net pen experiment. A total of 10 dietary treatments were compared. Nine diets were formulated to contain 363 g kg⁻¹ digestible protein and 14.8 MJ kg⁻¹ digestible energy, and a dietary treatment consisting of raw fish (RF) served as reference. In the formulated diets, the control diet contained 350 g kg⁻¹ herring meal, whereas in the other eight diets, the fishmeal were replaced by MBM (30% fishmeal replacement), PM (50% fishmeal replacement), a blend of PM, MBM, FM and BM (30%, 50% and 80% fishmeal replacement), or a blend of PM, MBM and BM (30%, 50% and 80% fishmeal replacement), respectively. Cuneate drum fingerling (initial body weight 28 g) were fed the test diets for 8 weeks. Specific growth rate (SGR), final body weight (FBW), nitrogen retention efficiency (NRE), condition factor and contents of moisture, crude protein and crude lipid in carcass were not significantly different between fish fed the formulated diets. Fish fed the formulated control diet exhibited lower SGR and FBW, but higher FCR, NRE, hepatosomatic index and crude lipid content in carcass and liver than those of the fish fed the RF. Results of the present study indicate that combination of rendered animal protein ingredients can replace most of the fishmeal in practical diets for cuneate drum.     

Effect of Replacing Menhaden Oil with Catfish Oil on the Fatty Acid Composition of Juvenile Channel Catfish, Ictalurus punctatus

The effect of using a finishing diet containing menhaden fish oil on the fatty acid composition of fingerling channel catfish, Ictalurus punctatus, was evaluated in a 12‐wk growth trial. Three isocaloric, isonitrogenous practical diets with three different sources of lipids (menhaden oil [MO], catfish oil [CO], or beef tallow [BT]) were formulated (35% crude protein). No differences in eicosapentaenoic acid, docosahexaenoic acid, or arachidonic acid were observed to occur in catfish fed MO or CO diets; however, these fatty acids were significantly lower in fish fed BT diet. No differences were observed for unsaturated fatty acid content in channel catfish fed a diet containing MO for 8 or 12 wk. In addition, no differences in production characteristics were observed to occur when catfish were fed diets containing CO, MO, or BT as the dietary lipid source, which indicates that BT, CO, and MO are equally effective as sources of energy. It is apparent from these results that CO may be successfully substituted for MO in formulated diets without adversely affecting n‐3 highly unsaturated fatty acid content in channel catfish.     

Effects of dietary fish oil replacement with vegetable oils on growth and tissue fatty acid composition of humpback grouper, Cromileptes altivelis (Valenciennes)

The replacement of dietary marine fish oil with vegetable oils was examined in fingerling humpback grouper, Cromileptes altivelis, over the course of an 8‐week growth trial. Five isolipidic (10%) and isoproteic (50%) fish meal‐based practical diets were formulated to contain iso‐ingredients but with different sources of lipids [crude palm oil (CPO), refined, bleached and deodorized, palm olein (RBDPO), soybean oil (SBO) or canola oil (CNO)], and their performance was compared with the control diet, which contained cod liver oil (CLO) as the added lipid source. The experimental diets were fed close to apparent satiation twice a day to triplicate groups of fish (10.6 ± 2.2 g). The grouper fingerlings were randomly distributed into groups of 12 fish in cylindrical cages (61 cm depth and 43 cm diameter) that were placed in a 150 tonne polyethylene seawater tank. There were no significant differences (P>0.05) in terms of growth, survival, feed conversion ratio, protein efficiency ratio, net protein utilization, hepatosomatic index and condition factor among fish fed the various dietary treatments. Similarly, the dietary lipid source did not significantly affect the whole body proximate composition of the fish. Muscle and liver fatty acid composition of fish was influenced by the experimental diets. Replacement of dietary CLO with CPO, RBDPO, SBO or CNO produced fish with lower n‐3 highly unsaturated fatty acids and increased levels of 18:2n‐6 in the muscle and liver. The n‐3:n‐6 fatty acid ratio in the muscle of fish fed the CLO‐based diet was 3.0 compared with 0.5–0.8 in the muscle of fish fed the various vegetable oil‐based diets. The present study demonstrated that various vegetable oils can be used in fish meal‐based dietary formulations for humpback grouper without compromising growth or feed utilization efficiency.     

Schizochytrium as a replacement for fish oil in a fishmeal free diet for jade perch,Scortum barcoo (McCulloch & Waite)

A 10‐week trial was conducted to determine the response of juvenile jade perch Scortum barcoo on the replacement of dietary fish oil (FO) in a fishmeal free diet. Three iso‐nitrogenous, isocaloric and isolipidic diets were formulated, each containing a different primary fat source: FO, linseed oil (LO), and a mixture of Schizochytrium and LO. The substitution of FO with the mixture of Schizochytrium and LO did not cause a difference in growth. However, there was an 8% reduction in weight gain in fish fed dietary LO, indicating that juvenile jade perch do require a minimal concentration of dietary n‐3 highly unsaturated fatty acids (HUFA). Fish fed the Schizochytrium diet stored more efficient n‐3 HUFA and in particular DHA in their flesh, and retained a higher fillet recovery compared to fish fed FO. In addition, we demonstrated that jade perch are able to produce both n‐3 HUFA and n‐6 HUFA when dietary PUFA are present. Fish fed the LO diet for 10 weeks contained the lowest amount of n‐3 HUFA in fillets among dietary treatment groups. However, feeding these fish the Schizochytrium diet for an additional 4 weeks increased the n‐3 HUFA content towards the same concentration of n‐3 HUFA found in the flesh of fish fed FO, without affecting the sensory properties of the fillets. In contrary, feeding the Schizochytrium diet for a continuous period of 14 weeks lowered overall sensory property scores.